Investigations of III-V concentrator solar cells with liquid immersion for high concentrating photovoltaic systems

Liquid-immersed III-V concentrator solar cells have been proposed either for providing a new concentrator with high optical performance or for solving the receiver thermal management issue under high concentration. In this paper, the behavior of III-V GaInP/GaInAs/Ge triple junction (TJ) solar mini-receivers immersed in white oils A/B/C, C14 n-alkane, C16 iso-alkane, and dimethyl silicone oil, respectively, is examined. A sizeable relative percentage increase (4.67-8.99%) in electrical conversion efficiency of TJ solar mini-receivers is found for 4-mm-thick liquid layers. Increasing the thicknesses of all the liquid candidates to approximately 9-10 mm continues to raise the efficiency of the corresponding TJ solar mini-receivers. The optical effect and the electrical effect contributing to the increase in efficiency, which is caused by the thin liquid layer on the solar cell front surface, are discussed. Further, to evaluate the durability of TJ solar mini-receivers operating in the examined liquids, UV exposure, damp heat, and step temperature accelerated lifetime tests on the liquid-immersed TJ solar mini-receivers were carried out. Results from the tests demonstrate the long-term stability of TJ solar mini-receivers operated in C14 n-alkane, C16 n-alkane and dimethyl silicone oil, respectively. They also indicate that among these the best liquids for immersing III-V concentrator solar cells is dimethyl silicone oil, followed by C14 n-alkane.